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United States Patent |
5,703,574
|
Allonen
|
December 30, 1997
|
Method and device for transferring a measurement signal from a revolving
roll used in a paper making machine
Abstract
A method and device for transferring a measurement signal from a revolving
roll used in a paper making machine, in which detectors are arranged in
the transverse direction of the roll, preferably uniformly spaced.
Measurement signals generated by the detectors are passed to a measurement
signal reading unit for reading the measurement of the detectors which is
installed preferably at the end of the roll. From the measurement signal
reading unit, the signals are transmitted wirelessly further as telemeter
signals to a reading unit which is placed outside the roll and connected
to a PC or equivalent computer. In the measurement signal reading unit for
reading the measurement of the detectors, a transponder is arranged into
which an unique code is coded for each detector. The signals are processed
in the entire measurement process as analog signals. In the transfer of
the telemeter signals between the unit for reading and measurement of the
detectors and the reading unit placed outside the roll, a substantially
low transfer frequency of an order of from about 100 kHz to about 150 kHz
is employed.
Inventors:
|
Allonen; Harri (Jyvaskyla, FI)
|
Assignee:
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Valmet Corporation (Helsinki, FI)
|
Appl. No.:
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213105 |
Filed:
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March 14, 1994 |
Foreign Application Priority Data
Current U.S. Class: |
340/870.07; 340/870.18; 340/870.19; 342/42; 342/51 |
Intern'l Class: |
G01S 013/75 |
Field of Search: |
340/870.18,870.16,870.05,870.07,870.19
73/862.55
100/50
162/198
342/42,51
|
References Cited
U.S. Patent Documents
4062005 | Dec., 1977 | Freed | 340/870.
|
4328494 | May., 1982 | Goodall | 340/870.
|
4399440 | Aug., 1983 | Douglas | 340/870.
|
4403218 | Sep., 1983 | Beal | 340/870.
|
4730183 | Mar., 1988 | Crowe | 340/870.
|
4791863 | Dec., 1988 | Vahatalo | 100/35.
|
4827395 | May., 1989 | Anders | 764/138.
|
4883233 | Nov., 1989 | Saukkonen et al. | 242/66.
|
4921183 | May., 1990 | Saukkonen et al. | 242/66.
|
5043046 | Aug., 1991 | Laapotti | 162/358.
|
Foreign Patent Documents |
924138 | Sep., 1992 | FI.
| |
914829 | Apr., 1993 | FI.
| |
9113337 | Sep., 1991 | WO.
| |
Other References
J. Koriseva, T. Kiema and M. Tervonen, "Soft Calender Nip:An Interseting
Subject For Research and Measurement", Paperi ju Paa (Paper and Timber,
vol. 73 (1991), No. 5.
|
Primary Examiner: Hofsass; Jeffery
Assistant Examiner: Wong; Albert K.
Attorney, Agent or Firm: Steinberg, Raskin & Davidson, P.C.
Claims
I claim:
1. In a method for transferring measurement signals generated by detectors
arranged on a revolving roll of a paper making machine to a first
measurement signal reading unit and wirelessly transmitting said signals
from said first measurement signal reading unit to a second reading unit
situated exterior to the roll and associated with a control unit, the
improvement comprising the steps of:
coupling a transponder to said first measurement signal reading unit,
coupling said transponder to each of said detectors such that said
transponder directs one of said detectors to generate a measurement signal
upon receipt of a unique code assigned to said one of said detectors,
reading analog measurement signals generated by said detectors by means of
said first measurement signal reading unit, and
transmitting said analog measurement signals from said first measurement
signal reading unit at a frequency in the range of between about 100 kHz
and about 150 kHz to said second reading unit.
2. The method of claim 1, further comprising the step of uniformly spacing
said detectors in a transverse direction of the roll.
3. The method of claim 1, further comprising the step of arranged said
first measurement signal reading unit at an end of the roll.
4. The method of claim 1, further comprising the step of converting said
analog measurement signals to a pulse form in said first measurement
signal reading unit, said measurement signals being transmitted by said
transponder in pulse form.
5. The method of claim 1, wherein said measurement signals are transmitted
by said transponder and are FSK-modulated signals.
6. The method of claim 1, further comprising the step of initiating
measurement via said detectors by directing a command from said second
reading unit to said transponder, the measurement unit otherwise remaining
in a passive state.
7. The method of claim 1, further comprising the steps of storing the
unique codes for each detector in said transponder, calibrating each
detector based on the stored codes, and identifying specific ones of said
detectors and reading measurements signals from the identified detector
based on the stored codes.
8. The method of claim 1, further comprising the steps of forming a nip
between the roll and an additional press roll, and measuring the
distribution of the compression pressure in the nip in a machine direction
thereof via said detectors.
9. The method of claim 1, further comprising the steps of forming a nip
between the roll and an additional press roll, and measuring the
distribution of the compression pressure in the nip in a transverse
direction via said detectors.
10. The method of claim 1, wherein the frequency for the transfer of said
measurements signals in pulse form from said first measurement signal
reading unit to said second reading unit is about 130 kHz.
11. The method of claim 1, wherein said transponder is provided with one of
the unique codes assigned to each of said detectors at each time to
conduct individual measurements by means of said detectors.
12. A device for transferring measurement signals generated by detectors
arranged on a revolving roll of a paper making machine to a first
measurement signal reading unit and wirelessly transmitting said signals
from said first measurement signal reading unit to a second reading unit
situated exterior to the roll and associated with a control unit,
comprising
a transponder arranged in said first measurement signal reading unit, said
transponder being coupled to each of said detectors and structured and
arranged to direct one of said detectors to generate a measurement signal
upon receipt of a unique code assigned to said one of said detectors, said
transponder comprising means for transmitting said measurement signals in
pulse form at a frequency in the range between about 100 kHz and about 150
kHz,
said first measurement signal reading unit comprising means for processing
said measurement signals received from said detectors as analog signals.
13. The device of claim 12, wherein said detectors are uniformly spaced in
a transverse direction of the roll.
14. The device of claim 12, wherein said first measurement signal reading
unit is arranged at an end of the roll.
15. The device of claim 12, wherein said detectors are activated by
directing a command to said transponder via said second reading unit, said
detectors otherwise being in a passive state.
16. The device of claim 12, wherein the unique codes of each of said
detectors is used to calibrate said detectors and for identifying a
specific detector to read the measurement signal generated by the specific
detector.
17. The device of claim 12, wherein said first measurement signal reading
unit further comprises means for converting said measurement signals in
analog form generated by said detectors to a pulse form.
18. The device of claim 12, further comprising an antenna coupled to said
second reading unit for receiving the wirelessly transmitted pulse form of
said measurements signals from said transponder.
19. The device of claim 12, wherein the frequency of the transfer of said
measurements signals in pulse form from said transponder to said second
reading unit is about 130 kHz.
20. The device of claim 12, wherein said transponder is provided with one
of the unique codes assigned to each of said detectors at each time to
conduct individual measurements by means of said detectors.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method for transferring a measurement
signal from a revolving roll used in a paper making machine, in which
detectors are arranged in the roll. The detectors are preferably uniformly
spaced over a desired width of the roll in a transverse direction thereof.
Measurement signals received from the detectors are passed to a
measurement signal reading unit for reading and measuring the measurements
signals generated by the detectors. The measurement unit is preferably
installed at one end of the roll and transmits signals wirelessly as
telemeter signals to a transponder reading unit which is placed outside
the roll and is connected to a control unit, e.g., a PC or to an
equivalent computer.
The present invention also relates to a device for transferring measurement
signals from a revolving roll used in a paper making machine. The device
comprises detectors arranged in connection with the roll, and which are
preferably uniformly spaced in the transverse direction of the roll. A
measurement signal reading unit for reading measurement signals generated
by the detectors is preferably installed at an end of the roll. Signals
received from the measurement detectors are passed to the measurement
unit. The device further includes a reading unit placed outside and
exterior to the roll. The measurement signal reading unit for reading
measurement signals from the detectors is arranged to transfer the
measurement signals to the outside reading unit as telemeter signals, as
well as a PC or an equivalent computer unit which is connected to the
reading unit.
In a number of different stages in the manufacture of paper, various nips
are used through which the paper web is passed. Examples of such nips
include roll nips and so-called extended nips in the dewatering presses in
a paper machine, calendaring nips, and the nips in paper reels. The
transverse distribution of the nip pressure in a dewatering press, i.e.,
the distribution of the nip pressure in the axial direction of the nip
rolls, affects the transverse moisture profile of the web that is being
pressed.
In the prior art, it is possible to use adjustable-crown rolls or
variable-crown rolls (so-called Kusters rolls) as the press rolls.
Transverse distribution of the linear load in the press nip can be
controlled by means of hydraulic loading members (in adjustable-crown
rolls) or by means of a chamber or a series of chambers pressurized by
means of hydraulic fluid (in variable-crown rolls). The hydraulic loading
members that are used in adjustable-crown rolls are usually regulated on
the basis of regulation signals given by moisture and/or grammage
detectors. However, in view of overall control and regulation of the
process, it would also be extremely important to determine and ascertain
the factual values and distributions of the nip pressure both in the
transverse direction and in the machine direction. An additional piece of
information which is important in view of the control of the nip process
is the width of the nip in the running direction of the web, i.e., in the
machine direction, on whose basis it is possible to optimize the pressing
process. This information is also a significant factor in the regulation
of the calender and reel nips. As an exemplifying embodiment of a system
of regulation of press nips, reference is made to the assignee's Finnish
Patent No. 76,872 (corresponding to U.S. Pat. No. 4,791,863, the
specification of which is hereby incorporated by reference herein). A
measurement system similar to the present invention may be used in the
environment of the sort described in this reference.
Recently, various so-called extended-nip presses based on press shoes
and/or on press bands have been introduced. In these extended nips, the
width of the press zone in the machine direction is substantially larger
than in roll nips proper. Also in extended-nip presses, the distribution
of the nip pressure in the shoe and/or band nips both in the machine
direction and in the transverse direction is an important parameter in
view of the control of the pressing process. As an example with respect to
extended-nip presses, reference is made to the assignee's Finnish Patent
No. 82,092 (corresponding to U.S. Pat. No. 5,043,046, the specification of
which is hereby incorporated by reference herein).
In the prior art, various drum reels are known, in which, besides the reel
drums, belt-support units have also been used. When reeling a paper web,
it is also important to know the values of the nip pressure and its
distributions both in the machine direction and in the transverse
direction. As some examples of the reels that have been developed by the
assignee, in connection with which it is possible to use the method and
the device of the present invention, reference is made to the assignee's
Finnish Patent Nos. 81,768 and 81,770 (corresponding to U.S. Pat. Nos.
4,921,183 and 4,883,233, respectively, the specifications of which are
hereby incorporated by reference herein).
By means of the prior art methods and devices, it has been practically
almost impossible to measure the distribution of the nip force both in the
machine direction and in the transverse direction during production
operation. However, this distribution is important in view of the
regulation and control of the paper making process. Measurement of the nip
forces from a revolving roll has been carried out under laboratory
conditions, in which respect reference is made to the paper in the journal
Paperi ja Puu --Paper and Timber 73 (1991): 5, by J. Koriseva, T. Kiema
and M. Tervonen: "Soft Calender Nip: an Interesting Subject for Research
and Measurement". In the method described in this paper, a number of
detectors are installed on the roll, each of which detectors requires a
telemetric equipment of its own and amplifiers of its own. Since the
weight of the measurement system mainly consists of the weight of the
telemetric equipment (about 1 kilogram per channel), this, together with
the high cost of such equipment, sets a limit on the number of measurement
channels and detectors in a roll of a factual paper machine or a paper
finishing machine. Moreover, owing to the limited space, it is very
difficult to install a large number of telemetric equipments on a
revolving roll in a paper machine or finishing machine without changes in
the construction of the machines.
With respect to the prior art related to the present invention, reference
is also made to published International Patent Application No. WO 91/13337
(in the name of Beloit Corp.).
In the prior art methods and devices for measuring nip forces, problems
have also been encountered in the calibration of the detectors and in the
transfer of the signal from a revolving roll. In the prior art, for the
transfer of the signal, glide rings and similar arrangements have been
used, and also telemetric equipments. However, it is a drawback that such
arrangements are complicated and susceptible to interference.
In order to eliminate the drawbacks of the prior art methods and device
described above, in the assignee's Finnish Patent Application No. 914829
(corresponding to published Finnish Patent No. 86,771 and U.S. Ser. No.
07/960,725 issued as U.S. Pat. No. 5,383,371, the specification of which
is hereby incorporated by reference herein), a method and device closely
related to the present invention are described in which the measurement
signals received from the different detectors are passed to a switching
unit. Connectors in the switching unit are controlled based on the
rotation of the roll, or equivalent, by means of a pulse generator or
equivalent so that, through the switching unit, the signal of each
measurement detector is alternatingly connected to a telemeter transmitter
placed in connection with the revolving roll or equivalent. By means of
the telemeter transmitter, the series of measurement signals are
transmitted wirelessly to a stationary telemeter receiver placed outside
the revolving roll or equivalent.
One of the objects of the invention described in Finnish Patent Application
No. 914829 is to provide a method and a device for measurement of the nip
forces and nip pressures and the distribution of the same in roll and/or
band nips that are used in the manufacture of paper so that the drawbacks
discussed above can be substantially avoided. The measurement method and
device of FI 914829 is suitable for on-line measurement of nip forces
and/or nip pressures during production operation, and the transfer of
signals from the revolving roll is solved in a simpler and more economical
way so that the method is suitable for an environment of paper
manufacture, which environment is quite demanding in this respect.
Further, in the method and device of FI 914829, the problems related to
the placing of the detectors on a nip roll and/or on a nip band are
substantially solved.
Even though the prior art methods and devices described above have proved
quite good and operable in comparison with earlier systems, some unsolved
problems have however remained. One particular problem consists of the
high frequencies employed in the transfer of signals from the detectors to
the measuring and reading units. Owing to the high frequencies, the signal
transfer distance may have to be quite long, but the long transfer
distance results in a relatively high susceptibility to interference. In
the earlier telemeter systems, the signal to be transmitted was already
converted to digital form at the roll-side end, the signal being then
transferred in the digital form (see, e.g., the assignee's Finnish Patent
Application No. 924138 of earlier date). Such a system has required a
relatively high number of complex electronic components which are arranged
on the roll. This has the consequence of the construction of the equipment
having a large size and high weight, frequently even a few hundred grams,
for which reason the roll has to be balanced separately for this purpose.
Further, the prior art systems of have involved the problem related to the
calibration of the measurement detectors. In the earlier systems, viz.,
the computer connected with the system, such as a PC or equivalent, had to
include an extensive and complex calibration program, which in most cases
was tailored for the specific case, in order that it was possible to
calibrate the detectors. The special required tailoring of a program also
constitutes an important cost factor.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method
and device more advanced than the methods and devices described in the
assignee's Finnish Patent Applications of earlier dates (Nos. 914829 and
924138), so that, compared with the methods and device of these earlier
patent applications, the method and device of the present invention are
simpler, easier to operate, more reliable in operation, and more
versatile. In particular with respect to the electronics, in the present
invention, attempts have been made to provide an embodiment that is
simpler and also involves lower costs in comparison with the assignee's
earlier inventions.
It is a further object of the present invention to provide a new and
improved measurement system that can be controlled in a simple way during
operation of the machine from outside the revolving roll so that, if
necessary, measurement data and calibration data can be supplied to the
measurement system from outside the roll and measurement data can be
transferred from the roll wirelessly to the outside system in this manner,
it is favorably possible to feed the measurement data into the regulation
system of the roll so that, in some cases, a closed regulation circuit can
be formed.
It is another object of the present invention to provide a new and improved
method and device for transferring measurement signals from detectors
arranged on a roll to a remote control unit in which a low transfer
frequency is used.
In view of achieving the objects stated above and others, in the method in
accordance with the present invention, a transponder is arranged in a
measurement signal reading unit which reads and processes the measurements
signal generated by the detectors. The transponder is provided with a code
representing each of the detectors. Signals from the detectors are
processed in the entire measurement process as analog signals. During the
transfer of the telemeter signals between the measurement signal reading
unit for reading the measurements of the detectors and a transponder
reading unit placed outside the roll, a substantially low transfer
frequency of an order of from about 100 kHz to about 150 kHz is employed.
The device in accordance with the present invention comprises a transponder
in itself known which is coded and arranged in the unit for reading and
measurement of the detectors. The transponder comprises means to process
the signals received from the measurement detectors as analog signals, and
in pulse form, the signals being transmitted in pulse form from the
transponder to an antenna of the transponder reading unit situated
exterior to the roll. The frequency of transfer of the telemeter signals
between the measurement signal reading unit for reading the measurements
of the detectors and the transponder reading unit placed outside the roll
is arranged to be substantially low, e.g., of an order of from about 100
kHz to about 150 kHz. The transponder comprise means to transmit the
telemeter signals at these low frequencies. Although the specified range
of frequencies is preferred,other transfer frequencies may also be used in
connection with the transponder herein.
By means of the present invention, compared with the prior art devices, a
number of advantages are obtained, of which the following advantages are
expressly stated. Compared with the prior art, the components included in
the system of the present invention are very small and have a low weight
so that they can also be fitted easily at the roll-side end without having
to balance the roll on their account. The power requirement of the system
is very little. The supply of current can be accomplished by means of a
very small battery because the system is not active all the same time. The
system is not activated until a separate command for this purpose is given
from the receiving end, i.e., the reading unit or the control means via
the reading unit. The measurement unit otherwise remains in a passive
state conserving electricity.
The measurement signal is transferred in the system in accordance with the
present invention as an analog signal and at a very low frequency (the
transfer frequency is of an order of from about 100 kHz to about 150 kHz,
preferably 130 about kHz). The signal to be transferred is FSK-modulated
(FSK=Frequency Shift Keying), in which case the transfer of the signal
takes place as an analog signal and in pulse form. By means of this
arrangement, the transfer of information can be made substantially free of
interference. When the signal is converted to pulse form in the
measurement unit, any interference can be easily filtered out, in which
case it is possible to read the main frequency alone.
In the system in accordance with the present invention, at the roll-side
end, a transponder is used, one of whose advantages over the earlier
systems is the ease of calibration of the detectors. This is based on the
fact that, in the transponder, it is possible to assign an individual and
unique code for each detector, by means of which code it is then simple to
compare the calibration of each detector. The possibility of coding also
simplifies and facilitates the use of the system, by means of the computer
or other control means, such as a PC (personal computer) or equivalent,
connected to the system. Through the read/write unit of the transponder,
it is possible to give the transponder a command to read a detector of a
certain code alone. As the detectors in the system, it is possible to use
PVDF-type film detectors or, for example, strain gauges or equivalent.
Further advantages and characteristic features of the invention will come
out from the following detailed description of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The following drawings are illustrative of embodiments of the invention and
are not meant to limit the scope of the invention as encompassed by the
claims.
FIG. 1 is a schematic side view of a press nip to which the method and
device equipment in accordance with the present invention are applied.
FIG. 2 is a schematic illustration of the distribution of the compression
pressure in the machine direction in a press nip as shown in FIG. 1.
FIG. 3 is a schematic illustration of the distribution of the compression
pressure in the transverse direction in a press nip as shown in FIG. 1.
FIG. 4 is a schematic illustration of a measurement arrangement in
accordance with the present invention as applied, e.g., to a nip roll in
the press nip shown in FIG. 1.
FIG. 5 is a schematic block-diagram illustration of the transfer of a
measurement signal in the method and device in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the accompanying drawings wherein like reference numerals
refer to the same elements, FIG. 1 is a schematic side view of a press nip
N in a dewatering press of a paper machine. The nip N is formed between
the rolls 10 and 13. In the press nip N, water is removed out of a web W
which is passed into the nip N on support of a press felt 12. The upper
roll, roll 10, in the dewatering press has a smooth outer face 10' and is
provided with an elastic coating 11. Onto the lower roll, roll 13, in the
dewatering nip, a hollow face 13' has been formed, into which water can be
removed out of the press felt 12.
FIG. 2 is a schematic illustration of the distribution of the compression
pressure P.sub.M in the press nip N in the machine direction l. The
maximum value of the compression pressure P.sub.M is denoted by the
reference P.sub.max. The nip N as shown in FIG. 1 may also represent a
calendaring nip, in which case a press felt 12 is not used and in which
case, e.g., the roll 13 is a hard-faced roll and the roll 10 is a
calendaring roll provided with a soft coating, such as a polyurethane
coating 11, so that the nip N is a so-called soft calendaring nip.
FIG. 3 illustrates schematically the distribution of the compression
pressure P.sub.T in the nip N in the transverse direction, i.e., in the
axial direction of the rolls 10 and 13. The transverse width of the paper
web W and of the nip N is denoted by reference L.sub.O. The transverse
distribution of the compression pressure P.sub.T affects the dry solids
content of the web in dewatering nips, the caliper and smoothness of the
web in calendaring nips, and the uniformity and the hardness profile of
the reel in reeling nips. These are important process quantities, so that
the distributions P.sub.M and P.sub.T of the nip forces and nip pressures
are important parameters for the regulation and control of the paper
making process.
FIG. 4 is a schematic illustration of the main principles of the
measurement arrangement in accordance with the present invention as
applied to one of the rolls 10 that form the press nip, the roll 20 being
provided with an elastic coating 11, e.g., of polyurethane. A number of
measurement detectors 5 are arranged inside the coating 11, and are
preferably arranged to be uniformly spaced in the axial direction of the
roll. By means of such a series of detectors 5 arranged at different
circumferential positions on the roll, it is possible to measure both the
distribution P.sub.M of the nip pressure in the machine direction and the
transverse distribution P.sub.T of the nip pressure. The transverse nip
pressure is measured at the points corresponding to the number of the
detectors 5 in the transverse direction. The detectors 5 may be attached
either directly to the body of the roll 10 or may be inlaid into the
coating 11, e.g., between different layers in the coating. In some
particular cases, it is possible to arrange the detectors 5 directly on
the outer face of the roll. The detectors 5 may also be arranged in
several positions along the circumference of the roll to provide
measurements in the machine direction of the roll.
Measurement signals are passed from the detectors 5 along cables 6 to a
unit 2 for reading the measurement of the detectors, referred to as a
measurement signal reading unit. Unit 2 is fixed to the end of the roll
near the roll axle 18. As shown in FIG. 5, the measurement signal reading
unit 2 for reading the measurement signals generated by the detectors
includes a voltage/frequency converter 21, through which signals
representative of, e.g., the pressure measurements from the detectors are
transferred further to the signal processing/analyzing electronics unit 22
integrated in the same unit 2. In the signal processing and analyzing
electronics unit 22, the signal is modulated by means of a frequency
modulator to FM-modulation into so-called FSK-modulated pulse form
(FSK=Frequency Shift Keying). The signal, which has been converted to this
form, is transferred further into the transponder 23, which is integrated
in the same unit 2 and capable of processing the FSK-modulated
pulse-formed signal. The transfer of the signal is constantly analogous,
and it is at no stage converted to digital form. The analog signal is just
converted to pulse form in the measurement signal reading unit 2 for
reading the measurements from the detectors, in which case it is easy to
filter off any interference so that the main frequency can be read.
The transponder 23 is of the read/write type and is arranged to both
receive and transmit signals. From the transponder 23, the signal is
transferred telemetrically to a transponder reading unit 3 by means of an
antenna 4.
As shown in FIG. 4, the transponder reading unit 3 is attached to the frame
14 of the bearing housing of the roll 10. The antenna 4 may be attached to
a face of the frame 14 of the bearing housing of the roll 10. In the
telemetric signal transfer, a low transfer frequency is used, which is
preferably of an order of about 130 kHz. The transponder reading unit 3
includes the electronics necessary for data transfer and, e.g., a
frequency/voltage converter, by whose means the transferred signal is
converted back to voltage form. The signal is converted to voltage form
because the PC computer 7 can process such a voltage form. From the
transponder reading unit 3, the signal is transmitted to the PC 7 along a
cable 8, so that the distance from the transponder reading unit 3 to the
PC 7 does not constitute a limiting factor in the system.
The transponder 23 is a commercially available component which has a very
small size and low weight, and is manufactured and marketed, e.g., by
Texas Instruments Corp. under the trade mark TIRIS. Such a transponder 23
can be coded so that it is possible to code (assign a code to) consisting
of a number of several digits, e.g., 20 digits, for each detector 5. In
such a case, the calibration of the detectors 5 can be carried out easily
and simply, because the calibration of each detector 5 can be compared
with the number coded in the transponder 23. Thus, the PC 7 does not have
to contain a large and complex calibration program for the detectors 5.
It is another advantage of the present invention that the use of the system
in accordance with the invention is very easy and simple, among other
things, especially because of the fact that the transponder 23 can include
a code of its own for each detector 5. Since both the measurement signal
reading unit 2 for reading the measurements of the detectors and the
transponder reading unit 3 are of the read/write type, from the PC 7,
through the transponder reading unit 3, the transponder 23 can be given a
command to read exclusively the detector 5 that has a certain code. In
such a case, the PC 7 may include, e.g., a program that gives commands to
read the detectors 5 in a certain sequence or at certain intervals.
Two-way communications are thus provided.
The power consumption of the measurement electronics is very little,
because the system is not active all the time. The system is, viz., not
activated until a separate command is given for activation from the
signal-receiving end (the reading unit or the control means coupled to the
receiving unit). Thus, the current supply can be arranged by means of a
very small battery having a corresponding low weight, and which can be
fixed in a simple manner to the roll end in connection with, or at the
vicinity of, the measurement signal reading unit 2 for reading and
measurement of the detectors. The detectors 5 can be made favorably out of
a PVDF-film (PVDF=polyvinylidenedifluoride), which is a piezoelectric
film. The PVDF-film is well suitable for a power or pressure detector
especially because, by means of such a film, with a force of just tens of
newtons an output voltage of the volt level is already obtained. As the
detectors, it is indeed also possible to use, e.g., strain gauges or
other, corresponding detectors of this type that are commonly used.
Besides measuring pressures and forces, the system of the present invention
can also be applied, e.g., to measure temperature at objects at which such
information is needed. Some possible objects of this type of application
are also, e.g., the headbox of a paper machine, in which the system can be
used for measuring the uniformity of the lip profile. Further, the system
can be applied, e.g., to monitoring the condition of bearings, in which
case the measurement can be carried out, e.g., as measurement of the
vibration level. The measurement system in accordance with the present
invention can also be arranged to collect information constantly and at
certain intervals. In such a case, when desired, it would be possible to
look via the PC 7 what has happened in the object to be measured within a
certain period of time. In such a case, the measurement system would
operate in the way of a "black box".
Thus, in accordance with the invention, individual codes for each detector
can be stored in the transponder and each of the detectors can be
calibrated based on the stored individual codes. Moreover, during
measurement operations, specific ones of the detectors can be identified
by means of the individual codes so that measurements signals from the
identified detector can be read and processed.
The examples provided above are not meant to be exclusive. Many other
variations of the present invention would be obvious to those skilled in
the art, and are contemplated to be within the scope of the appended
claims.
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